This app continuously captures camera images in the background for timelapse videos (see video link for a sample).

Delay between images is adjustable down to 1 second.
Normal phone operation can continue with minimal CPU load.

Note: images are saved on SD card in an intermediate format to minimize CPU load. Use "Convert All" to convert them to PNG (warning: may take some time).

This app is open-source under GPL. The source code is available at https://github.com/floe/Background-Timelapse

I have a couple of additional features planned - please stay tuned :-)